The costs shown below are what I paid. Your costs will vary,
depending on where you buy your parts. 1. The overall cost of the secondary coil is $25.00. 2. The overall cost of the primary coil is $6.00 3. The overall cost of the safety gap is $2.00 4. The overall cost of the spark gap is $14.00 5. The overall cost of the power supplies varies. I got the 6,000
volt transformer at All Electronics for $20.00, though they are
now sold out.

If you can't find anything locally, there's always eBay. They aren't exactly popular there
(I mean, doesn't everybody own a 9KV transformer???), so the prices should be
decent, about $10 for a 6KV, 30mA transformer. I just got a two
transformers off eBay, totaling around $25, plus $13 to ship.
They were, both at 30mA each, 6000 volts, and 9000 volts. I
hooked up the 6KV one today. Nice! Got some good 3 inch sparks
off the thing. I think I need to make the primary coil a bit
bigger though.High Voltage Transformer Category

The overall cost of this Tesla Coil, including any extra costs,
can vary. But I figure it to be between $60 and $80.